(1) Field of the Invention
The present invention relates to a plasma processing apparatus that provides microfabrication in a semiconductor manufacturing process, and more particularly to a plasma processing apparatus having a temperature control unit for exercising temperature control over an electrode section that retains and locks a semiconductor wafer.
(2) Description of the Related Art
Temperature management of a currently processed wafer is important when a plasma processing apparatus processes the micropattern of a wafer surface with high precision. If the wafer surface temperature can be optimally controlled in accordance with the progress of a process, it is possible to not only increase processing accuracy but also enhance selectivity and throughput. At present, the high-frequency power applied to the plasma processing apparatus tends to increase with an increase, for instance, in the area of a wafer. For dielectric film etching, particularly, large power on the order of kilowatts is applied to increase the etching rate. When large power is applied, the ion impact energy relative to the wafer increases to increase the heat input to the wafer. Since the heat input to the wafer is increased as described above, an electrostatic adsorption electrode for retaining the wafer for temperature adjustment purposes needs a temperature control unit that supports high heat input and high-speed temperature control.
When the wafer temperature is to be controlled within the plasma processing apparatus, the temperature of the electrostatic adsorption electrode, which comes into contact with a wafer back surface, should be controlled. When a conventional electrostatic adsorption electrode is used, the electrode temperature is controlled by forming a refrigerant flow path within the electrode and causing a liquid refrigerant (e.g., Fluorinert (registered trademark)) to flow in the flow path. The liquid refrigerant is adjusted to a target temperature by a cooling device or heating device in a refrigerant supply unit (e.g., chiller unit) and then supplied to the electrode flow path. The aforementioned refrigerant supply unit is structured so as to store the liquid refrigerant in a tank and then discharge the liquid refrigerant after temperature adjustment. Since the liquid refrigerant has a large heat capacity, the refrigerant supply unit is instrumental in maintaining a constant wafer surface temperature. However, the refrigerant supply unit is poor in temperature response, cannot readily provide high-speed temperature control, and has low thermal efficiency. Therefore, it is demanded that the size of the refrigerant supply unit be increased to provide support for recent heat input increase.
Under the above circumstances, a direct expansion type refrigerant supply unit is proposed. The electrostatic adsorption electrode of the proposed refrigerant supply unit is provided with a compressor, which uses a refrigerant circulation system to pressurizes the refrigerant; a condenser, which condenses the pressurized refrigerant; and an expansion valve, which expands the refrigerant. The proposed refrigerant supply unit uses evaporative latent heat of the refrigerant to cool the electrostatic adsorption electrode. The direct expansion type refrigerant supply unit (or refrigeration cycle) makes it possible to control the semiconductor wafer temperature prevailing during a high heat input etching process at high speed and with high efficiency.
A method proposed, for instance, by Japanese Patent No. 3377830 adjusts the refrigerant evaporation temperature in the electrostatic adsorption electrode to a high temperature by sending a high-temperature refrigerant from a high-pressure side to a low-pressure side directly (without via a condenser or expansion valve).
A method proposed, for instance, by Japanese Patent Application Laid-Open Publication No. 2005-89864 heats the refrigerant with a heater installed in a refrigerant supply path to the electrostatic adsorption electrode.